This application claims benefit of Japanese Applications No. H11-343691 filed in Japan on Dec. 2, 1999 and No. H11-368189 filed on Dec. 24, 1999, the contents of which are incorporated by this reference.
1. Field of the Invention
The present invention relates to an electric operation apparatus, and more particularly to an electric operation apparatus and an output control method featuring a specific output control section for high frequency current.
2. Description of the Related Art
Electric knives and other types of electric operation apparatus are commonly used to incise or coagulate biological tissue, to stop bleeding, or to perform other procedures when internal or external surgery is conducted.
Such an electric operation apparatus comprises a high frequency cauterizing power supply unit and a treatment means connected to the high frequency cauterizing power supply unit, with the aforementioned treatment being performed by the application of the treatment means to the patient and feeding high frequency power from the high frequency cauterizing power supply unit.
Various proposals have been made concerning the aforementioned electric operation apparatus. For example, Japanese Patent Laid-open No. H8-98845 discloses a technique in which coagulation completion is verified on the basis of tissue impedance, and high frequency output is stopped in order to prevent the coagulating tissue from carbonizing and adhering to electrodes.
A technique for reducing the high frequency output in order to achieve the same object as in Japanese Patent Laid-open No. H8-98845 is also disclosed in connection with the electric operation apparatus described in Japanese Patent Laid-open No. H10-225462.
It should be noted that tissue impedance varies more rapidly with a reduction in the contact area between the tissue and the electrodes.
The electric operation apparatus described in Japanese Patent Laid-open Nos. H8-98845 and H10-225462 are configured such that, in case a narrow contact area is formed between the tissue and the electrodes, the tissue, sometimes, carbonizes or adheres to the electrodes while tissue impedance is measured or coagulation completion is verified.
Japanese Patent Laid-open No. H10-225462 discloses a technique in which the output of a high frequency current is reduced without being stopped after coagulation completion has been verified. According to this technique, a treatment can be continued if a surgeon or other specialist determines that insufficient coagulation has been achieved following verification of coagulation made by an electric operation apparatus. In the process, tissue degeneration can be slowed down due to reduced high frequency output, and the specialist can terminate the treatment once the desired coagulation state has been achieved.
However, the small size of the contact area between the tissue and the electrodes speeds up tissue degeneration and makes it more difficult for a specialist to terminate treatment once the desired coagulation state has been achieved. Another drawback is that a large contact area results in excessively slow tissue degeneration, and takes too long to obtain the desired coagulation state.
Yet another feature is that reducing the contact area between the tissue and the electrodes tends to make impedance, electric current, and the like susceptible to the influence of electrode operation and the like, and allows these parameters to be affected by factors unrelated to the coagulation state of the tissue.
The electric operation apparatus disclosed in Japanese Patent Laid-open Nos. H8-98845 and H10-225462 are disadvantageous in that when a small contact area is formed between the tissue and the electrodes, measurement results concerning electric current and the like become unstable and coagulation is sometimes considered to be complete even though in reality it is not.
An object of the present invention, which was accomplished in view of the above-described situation, is to provide an electric operation apparatus and an output control method that make it possible to consistently verify coagulation completion and to prevent tissue from carbonizing or adhering to electrodes irrespective of the size of the contact area between the tissue and the electrodes.
Another object of the present invention is to provide an electric operation apparatus and an output control method that allow the tissue degeneration rate to be kept within a range readily discernible by the specialist and the coagulation state to be easily identifiable irrespective of the size of the contact area between the tissue and the electrodes.
Yet another object of the present invention is to provide an electric operation apparatus and an output control method that prevent tissue from carbonizing or adhering to electrodes and that allow coagulation and other types of therapeutic treatments to be consistently performed even with a variable contact area.
Aimed at attaining the stated objects, the electric operation apparatus of the present invention comprises a high frequency current generating circuit for generating high frequency current and feeding this high frequency current to electrodes, and a direct current power supply circuit for feeding power to the high frequency generating circuit. With the direct current power supply circuit, the power being fed is variable. The electric operation apparatus also has a therapeutic condition monitoring circuit for monitoring the therapeutic condition induced by the high frequency current on the basis of the high frequency current outputted by the high frequency current generating circuit, and a supplied power setting circuit for feeding a setting signal for the power supply to the direct current power supply circuit on the basis of the monitoring results obtained by the therapeutic condition monitoring circuit.
The inventive output control method for an electric operation apparatus involves using an electric operation apparatus comprising a high frequency current generating circuit for generating high frequency current and feeding this high frequency current to electrodes, and a direct current power supply circuit for feeding power to the high frequency generating circuit, wherein the direct current power supply circuit is such that the power being fed is variable. In addition, the therapeutic condition induced by the high frequency current is monitored on the basis of the high frequency current outputted by the high frequency current generating circuit, and a setting signal for the power supply is fed to the direct current power supply circuit on the basis of the monitoring results.
In more specific terms, the therapeutic condition monitoring circuit determines the therapeutic condition by comparing the current high frequency electric current value with a preset threshold value. The supplied power setting circuit compares the high frequency current with a preset target value and changes the setting signal to reduce the power supply to a prescribed level if it is verified based on the comparison results that the coagulation treatment has been completed. The target value is determined based on the maximum value of the high frequency current. The therapeutic condition monitoring circuit also determines the therapeutic condition by using the thickness of tissue between at least two electrodes for transmitting the high frequency current to a subject""s tissue. The therapeutic condition monitoring circuit determines the therapeutic condition by comparing the impedance value of the subject being treated with the threshold value established based on thickness. The threshold value is selected based on the minimum value of the impedance value thus measured. The therapeutic condition monitoring circuit determines the therapeutic condition on the basis of the amount of time corresponding to variations in the electric current value sampled. The therapeutic condition monitoring circuit determines the therapeutic condition on the basis of the time needed to achieve the maximum value of the electric current value thus sampled. The supplied power setting circuit compares the current value of the high frequency current with a threshold value established based on the aforementioned maximum value, and changes the setting signal in order to reduce the power supply on the basis of the comparison results. The supplied power setting circuit determines whether the high frequency electric current value has reached a preset threshold value after a predetermined time indicating the end of a blood coagulation treatment has elapsed, and changes the setting signal in order to reduce the power supply if it is established that coagulation has indeed occurred. The therapeutic condition monitoring circuit determines the therapeutic condition on the basis of the amount of time corresponding to variations in the sampled impedance value of the subject being treated. The therapeutic condition monitoring circuit determines the therapeutic condition on the basis of the time needed for the sampled impedance value of the subject being treated to reach its minimum value. The supplied power setting circuit compares the current impedance with a threshold value established based on the aforementioned minimum value, and changes the setting signal in order to reduce the power supply on the basis of the comparison results. The supplied power setting circuit determines whether the impedance value has reached a preset threshold value after a predetermined time indicating the end of a blood coagulation treatment has elapsed, and changes the setting signal in order to reduce the power supply if it is established that coagulation has indeed occurred.